BAF Plant: Use of BAF Plants for Leachate Treatment. A BAF Leachate Treatment Plant would be likely to comprise a two or three-stage aerobic bioreactor system, with pre-aeration and possibly flocculation, before the BAFUnit which forms the core treatment stage of the system. Tertiary treatment would be provided after the BAFunit in much the same way as in other biological systems. The BAFUnit is an ... leachate.co.uk